A well known toothed epicyclic gear comprises a housing, a central internally toothed ring gear fixed therein, a central gear and a carrier with planet gears. Improvement of load bearing capacity of such gear without increasing its radial dimension may be achieved by increasing the axial length of the toothed gears. However, when the axial length to diameter ratio of a planet gear exceeds 1.5, such increase becomes ineffective due to the unequal distribution of load along the tooth.
It is known to use an epicyclic gear comprising several rows of planet gears with a common carrier, with central ring gears axially movably mounted on a cylindrical link, and a load balancing unit for balancing load among the rows of planet gears, said unit arranged in the form of spacing disks, mounted on straight-toothed splines on the cylindrical link and having flanking cams with a slanting profile. The central ring gears are freely mounted on the cylindrical link and also have flanking cams with a slanting profile, which interact with the cams of the spacing disks.
Such arrangement has drawbacks, such as complexity of manufacture—additional processing of the splines on inner and outer cylindrical surfaces of the parts, as well as of the cams on their flanking surfaces; increased radial dimensions due to flanking cams and rings; limited accumulated teeth misalignment, which may be compensated as an error by said balancing unit.
It is also known to use toothed epicyclic gears comprising a sun gear, a crown gear and a carrier with, each of said planet gears consists of two separate toothed gears, the flanking surfaces of which are pressed to each other by means of springs, one of said toothed gears interacting with the sun gear and the other one—with the crown gear. Frictional bond in the contacts of separate gears provides a balanced distribution of load among all engagements in the planet gear.
A drawback of such arrangement consists in an unavoidable increase in the radial dimensions of the planet gears and hence of the whole gear. Axial dimensions of such gear are also large, as its planet gears need to be twice as wide as the traditionally used ones.
It is further known to use a multiple-row epicyclic gear comprising a housing, a composite internally toothed central gear, a carrier with rows of planet gears mounted thereon. In this context the term “composite” denotes a central gear made up of multiple assembled component parts. Each of said planet gears includes axially spring loaded externally toothed friction disks. The internally toothed central gear is composite, having major crowns and friction spacer rings arranged between said crowns. Said major crowns and friction spacer rings of the central gear are mounted in the housing in an axially movable manner and are axially spring loaded. Friction interaction between major crowns and friction spacer rings is performed on flat end faces. The toothed crowns of the central gear are connected with the latter by means of keys or spline connections, causing disadvantages of such arrangement, because, on the one hand, such arrangement is characterized by lower production efficiency due to the need for processing the splines, and, on the other hand, radial dimensions become larger. Besides, the contact between the frictionally contacting elements is performed on flat end faces. Powerful and therefore large hold-down units are required to achieve the necessary interaction force.